A typical prior art optical scanner is disclosed in German patent publication DE-OS 32 33 232. It consists essentially of a console-like housing having an elastic support surface for the document to be scanned, a transparent plate holding down the document, and an optical scanning head which can be moved across the plate. The scanning head is guided via parallel lateral supports on rails in the housing and is moved in the scan direction via a motorized rope mechanism rope.
Such a prior art apparatus must be installed at a fixed location. The size of the documents is limited by the size of the attached support surface. Thus, it is not readily possible to scan and display parts of large-size documents. The entire surface of a document is scanned in a single scanning operation.